The present invention is directed to the preparation of copper complex disazo dyestuffs. It is an improved process for the preparation of the dyestuff set forth below.
The 1:1 copper complex disazo dyestuff of the metal-free disazo compound of the formula (written in the form of the free acid): ##STR2## is known and its preparation is disclosed in Example 12 of U.S. Pat. No. 3,364,194. It comprises a two-step coupling reaction followed by copperization wherein 2-naphthylamine-4,8-disulfonic acid, after diazotization in aqueous acid solution is coupled with resorcinol to give a monoazo compound. The monoazo compound is salted out, isolated by filtration, and then added, in the form of the moist filter cake, to a neutral, aqueous solution of the diazonium salt of 2-amino-4-(beta-sulfatoethylsulfonyl)phenol. The second coupling reaction is carried out at a pH between 6.5 and 7.5. Copper sulfate is added to the resulting metal-free disazo dyestuff and the latter is converted into its copper complex compound at a pH between 5 and 6.
The 2-amino-4-(beta-sulfatoethylsulfonyl)-phenol starting material for the second diazo component of Example 12 is prepared by esterifying 2-amino-4-(beta-hydroxyethylsulfonyl)-phenol in an excess of concentrated sulfuric acid and subsequently diazotizing the product in an aqueous medium. The pH of the diazonium salt solution is then adjusted to a value between 6.5 and 6.8 with sodium bicarbonate.
A similar preparation method is disclosed in Example 17 of U.S. Pat. No. 4,334,076 by starting from 2-amino-4-(beta-sulfatoethylsulfonyl-phenol with nearly equivalent amounts of a sulfating agent, such as concentrated sulfuric acid or sulfuric acid containing sulfur trioxide, in a machine operating with a kneading action.
These prior art processes have several disadvantages:
(1) The monazo compound of the formula (Written in the form of the free acid) ##STR3## couples with the diazonium compound of 2-amino-4-(beta-sulfatoethylsulfonyl)-phenol only very slowly. The second coupling reaction requires a reaction time of about 24 hours;
(2) The synthesis of 2-amino-4-(beta-sulfatoethylsulfonyl)-phenol is somewhat difficult in that it requires several reaction steps involving a high investment for equipment. In its preparation, it is necessary to start from 2-nitro-4-(beta-hydroxyethylsulfonyl)-anisole which is dealkylated by heating with aqueous sodium hydroxide solution to give 2-nitro-4-(beta-hydroxyethylsulfonyl)-phenol. The resulting phenol is then reduced to give 2-amino-4-(beta-hydroxyethyl-sulfonyl)-phenol which, in turn, must be sulfated in accordance with the disclosure of U.S. Pat. Nos. 3,364,194 or 4,334,076.
U.S. Pat. No. 3,457,251 discloses the preparation of copper, cobalt and chromium complex disazo dyestuffs. Ring substituents capable of forming metal complexes are disclosed to be first the hydroxyl group, further the carboxyl group and the alkoxyl groups. According to Example 1 of this patent the monoazo reaction product of 3-amino-5-hydroxynaphthalene-7-sulfonic acid and 1-amino-8-hydroxynaphthalene-2,4 disulfonic acid is coupled with 2-amino-1-methoxybenzene-4-beta-hydroxyethyl sulfone - sulfuric acid ester and the resulting disazo dyestuff copperized by demethylating the methoxy benzene by the addition of copper sulfate (1.73 molar amount) and reacting for 15 hours at the boil. No examples of disazo dyestuffs of resorcinol are disclosed.